python - Django 数据迁移类型转换问题

Question

尝试将数据从 CharField 数据迁移到表中的 FloatingField。新的 floatingField 有 Null=True。在 python manage.py migrate.I 得到 ValueError: could not convert string to float:迁移文件如下所示。

def coordinates(apps, schema_editor):
    # We can't import the Person model directly as it may be a newer
    # version than this migration expects. We use the historical version.
    Restaurant = apps.get_model("foodspots", "Restaurant")
    for restaurant in Restaurant.objects.all():
        restaurant.lat_duplicate = restaurant.lat
        restaurant.lng_duplicate = restaurant.lng
        restaurant.save()


class Migration(migrations.Migration):

    dependencies = [
        ('foodspots', '0028_auto_20160211_1931'),
    ]

    operations = [
        migrations.RunPython(coordinates),
    ]

CharFields 的值类似于 10.787878。因为它们都是坐标。有些字段也有空值。我如何将它保存在表的 FloatingField 列中。数据库是 postgres

Answer 1

您必须在迁移中自己进行转换:

for restaurant in Restaurant.objects.all():       
    restaurant.lat_duplicate = float(restaurant.lat)
    restaurant.lng_duplicate = float(restaurant.lng)
    restaurant.save()

请注意，如果您的字段为 NULL 或包含空字符串或不是可接受的 float 表示形式的字符串，您将必须正确处理这些情况:

for restaurant in Restaurant.objects.all():       
    # minimalistic error handling
    try:
        restaurant.lat_duplicate = float(restaurant.lat)
        restaurant.lng_duplicate = float(restaurant.lng)
    except (TypeError, ValueError) as e:
        print "invalid type or value for restaurant %s : %s" % (
            restaurant, e
            )
    else:   
        restaurant.save()